Streptomyces griseus protease B, a member of the chymotrypsin superfamily, is encoded by a gene that expresses a pre-pro-mature protein. During secretion the precursor protein is processed into a mature, fully folded protease. In this study, we constructed a family of genes which encode deletions at the amino-terminal end of the propeptide. The secretion of active protease B was seen to decrease in an exponential manner according to the length of the deletion. The results underscore the intimate relationship between folding and secretion in bacterial protease expression. They further suggest that the propeptide segment of the zymogen stabilizes the folding of the mature enzyme through many small binding interactions over the entire surface of the peptide rather than through a few specific contacts.